The raven heir - Stephanie Burgis

Cordelia and her triplets Rosalind and Giles have lived safely in the castle at the centre of the forest all their lives, protected by the spells their mother has woven. The only time Cordelia feels truly free is when she turns into a dragonfly or a blackbird and can fly beyond the great stone walls. But then one day the outside world comes to them. Two rival dukes and their soldiers have come for the triplets - because whoever is the eldest is the heir to the throne.But their mother knows that since the Raven Crown was broken, no one has been able to rule the kingdom of Corvenne and live, and she will not give up any of her children to that death sentence. When she refuses to reveal which child is the eldest, she is taken prisoner, and Cordelia and her brother and sister find themselves on the run in a dangerous new world. And as they set out across Corvenne to rescue their mother, Cordelia begins to see that there is a deep magic at work, driving her towards a destiny that could tear her family apart, take away her freedom forever or, just maybe, heal a kingdom devastated by a war that has raged for generations.